1. Field of the Invention
The present invention relates to the intake system of an internal combustion engine, and more particularly to an intake duct in which fuel system parts such as a fuel supply pipe and a fuel injection valves are disposed at the an upstream side of an air cleaner.
2. Description of Related Art
When fuel temperature rises during an engine stop page fuel, vapor is generated. As a result, fuel supply to the engine becomes unstable in engine re-starting, and a defective engine start may be caused. To prevent this problem, it is necessary for the fuel temperature supplied to the engine to be maintained as low as possible to suppress vapor from being generated.
Conventionally, various methods of cooling fuel system parts such as the fuel injection valves, by means of engine intake air have been proposed. For example, in EP-0523027A2 and JP-A-63-100269, a fuel supply device such as the fuel injection valve is located within the air cleaner, so that the fuel supply device such as the fuel injection valve is cooled by intake air flowing through the air cleaner.
Further, in JP-U-63-183365, a fuel supply device including a fuel injection valve and a fuel supply pipe is disposed within a duct placed between the downstream side of an engine air cleaner and the upstream side of an intake manifold, so that the fuel supply device is cooled by intake air flowing through the duct.
However, in EP-0523027A2 and JP-A-63-100269, because the fuel supply device such as the fuel injection valve is located within the air cleaner, the locations where the air cleaner can be mounted are restricted due to the restriction of where the fuel supply device such as the fuel injection valve can be mounted. That is, the air cleaner is not freely located, and it is difficult for the air cleaner to be located in, for example, a narrow engine compartment of a vehicle.
Further, in JP-U-63-183365, since the fuel supply device is disposed within duct located downstream of the engine air cleaner, clean intake air passes through the duct. Therefore it is necessary for connections with the fuel supply device to have a strictly-airtight structure to prevent the in flow of polluted outside air which is not filtered. Thus, product cost becomes high, with the result that the method is not practically employed. In JP-P-63-100269, the fuel supply device is also located downstream of the air cleaner filter thereby causing the same problems.